It is known to use acoustic waves, such as ultrasonic energy, to determine information about an object. For example, in non-destructive testing, ultrasonic energy pulses are used to determine whether flaws exist in an object without damaging the object. Ultrasonic energy pulses are also used to obtain information about the friction ridge surfaces, such as fingerprints, of human beings.
To use an ultrasonic energy pulse to obtain information, the pulse must be sent from a device (the “emitter”) that is suitable for emitting ultrasonic energy pulses toward an object to be analyzed, and there must be a device (the “receiver”) that is suitable for receiving the energy once it has been reflected by or passed through the object. For ease of description, we will discuss the situation in which ultrasonic energy is reflected, but it will be recognized that this description can be applicable to situations in which the detected ultrasonic energy passes through the object being analyzed. Furthermore, in order to illustrate the concepts and ideas, the object being analyzed is from time to time described as a fingerprint, but it will be recognized that this invention is not limited to fingerprint scanners.
When the object being analyzed is a fingerprint, a single device can be used to serve as both the emitter and the receiver. Usually, the emitter and the receiver are positioned some distance from the object being analyzed, and so the emitted ultrasonic energy and the reflected ultrasonic energy must travel through a transmittive substance. Air is a transmittive substance for ultrasonic energy, but other substances transmit ultrasonic energy better than air. One such transmittive substance is mineral oil.